The present invention relates a method for producing bis(hydroxy-aromatic) compounds. More particularly, it relates a method for producing bis(hydroxy-aromatic) compounds in a catalytic reductive coupling reaction using hydrogen as the reductant.
Bis (hydroxy-aromatic) compounds find many uses in chemical applications, such as in dyes, plastics, pharmaceuticals and agrochemicals. In particular applications bis(hydroxy-aromatic) compounds are common monomers for use in forming polymers, such as polycarbonates, polyestercarbonates, polyesters, polyethers, polyetherimides, polyether ketones, polyetheretherketones and the like. Methods to produce bis(hydroxy-aromatic) compounds by reductive coupling of halo-substituted hydroxy-aromatic compounds are known in the art. The use of hydrogen as the stoichiometric reductant in such coupling reactions is also known. Busch et al. in Chemische Berichte, vol. 62, pp. 2612-2620 (1929) and in J. Prakt. Chem., vol. 146, pp. 1-55 (1936) describe a reductive coupling method for producing biaryl compounds from halo-substituted aromatic starting materials. The method uses high pressure hydrogen as reductant. However, halo-substituted aromatic starting materials also bearing polar substituents give lower selectivity to biaryl product. For example 4-bromophenol gives only 13% of 4,4xe2x80x2-dihydroxybiphenyl. Therefore, there is a continuing need for methods to synthesize bis(hydroxy-aromatic) compounds which provide high conversion of starting material and high selectivity to bis(hydroxy-aromatic) compound product.
The present inventors have discovered a method to prepare bis(hydroxy-aromatic) compounds by reductive coupling of halo-substituted hydroxy-aromatic compounds using hydrogen as a reductant at low pressure. The use of low pressure hydrogen reductant provides surprisingly high levels of both starting material conversion and also selectivity to the desired bis(hydroxy-aromatic) product. The use of low pressure also conserves hydrogen reactant and obviates the need for expensive high pressure reaction equipment. The use of low pressure hydrogen reductant also allows halo-substituted hydroxy-aromatic compounds with less reactive chloro-substituents to be used as starting materials.
In one of its embodiments the present invention comprises a method for preparing a bis(hydroxy-aromatic) compound which comprises the step of: contacting at least one halo-substituted hydroxy-aromatic compound in a solvent mixture comprising water and at least one organic solvent in the presence of at least one base, at least one catalyst comprising palladium and hydrogen gas at a pressure in a range of between atmospheric pressure and 350 kilopascals
Various other features, aspects, and advantages of the present invention will become more apparent with reference to the following description, examples, and appended claims.